net/bnx2x: fix build with GCC 11

net/bnx2x: fix build with GCC 11

Reproduced with '--buildtype=debugoptimized' config,
compiler version: gcc (GCC) 12.0.0 20210509 (experimental)

Build error:
In file included from ../drivers/net/bnx2x/bnx2x.c:16:
../drivers/net/bnx2x/bnx2x.c: In function ‘bnx2x_hc_ack_sb’:
../drivers/net/bnx2x/bnx2x.h:1528:35:
         warning: ‘igu_ack’ is used uninitialized [-Wuninitialized]
 #define REG_WR32(sc, offset, val) bnx2x_reg_write32(sc, (offset), val)
                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../drivers/net/bnx2x/bnx2x.h:1531:33:
	note: in expansion of macro ‘REG_WR32’
 1531 | #define REG_WR(sc, offset, val) REG_WR32(sc, offset, val)
      |                                 ^~~~~~~~
../drivers/net/bnx2x/bnx2x.h:1916:9: note: in expansion of macro ‘REG_WR’
 1916 |         REG_WR(sc, hc_addr, *val);
      |         ^~~~~~
../drivers/net/bnx2x/bnx2x.h:1905:33: note: ‘igu_ack’ declared here
 1905 |         struct igu_ack_register igu_ack;
      |                                 ^~~~~~~

REG_WR32 requires 'uint32_t', use union instead of cast to 'uint32_t'.

Bugzilla ID: 692
Fixes: 38dff79ba736 ("net/bnx2x: update HSI")
Cc: stable@dpdk.org
Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Kevin Traynor <ktraynor@redhat.com>